Composite target structure for television,x-ray and ultrasound camera tube



April 7, 1970 1. E. JACOBS COMPOSITE TARGET STRUCTURE FOR TELEVISION, x-RAY AND ULTRASOUND CAMERA TUBE Flled Sept 22 1966 layer' ayer /NVE/VTR JOHN E. JACOBS BY ym United States Patent O 3,505,558 COMPOSITE TARGET STRUCTURE FOR TELE- VIIJSION, X-RAY AND ULTRASOUND CAMERA T BE John E. Jacobs, 631 Milburn, Evanston, Ill. 60201 Filed Sept. 22, 1966, Ser. No. 581,351 Int. Cl. H013' 31 /48 U.S. Cl. 315--11 4 Claims ABSTRACT F THE DISCLOSURE A highly sensitive electron tube apparatus for converting X-ray or ultrasound images to viewable television images. Said electron tube having a target in which the electrical charge storage function is separated from the energy conversion function. Said target having a first layer of high dielectric material scanned by an electron beam. The ultrasound sensitive embodiment of the target having a piezo-resistive layer overlying said first layer. The X-ray sensitive embodiment of the target having a layer of gas which is rendered conductive by photo-electrons, and a layer of metal which emits photo-electrons into said layer of gas when excited -by X-ray energy. Also, methods for converting ultrasound and X-ray images to viewable television images by means of said apparatus.

This invention relates to image transducing electron tubes. More specifically, it relates to tubes for converting optical, X-ray or ultrasound images into corresponding electric signals.

Television image transducing tubes employing photoconductive targets and identified as VidiCons are well known in the art. None, however, has proven to be completely satisfactory, due to a necessity to compromise resistivity of the target material with sensitivity characteristics in order to obtain suitable storage characteristics of the target, and due to the necessity for relying on complex components which must be accurately dimensioned and precisely controlled in order to achieve the desired result. It is the aim of the present invention to overcome such disadvantages of prior art structures.

It is a principal object of the present invention to provide an image transducing electron tube with an improved target of uncomplicated construction and in which the storage feature and the sensitivity feature are effectively separated, thereby allowing the most effective utilization of each feature for optimum total performance.

Another object of this invention is to provide an improved light-sensitive television camera tube.

Another object of this invention is to provide an irnproved highly sensitive apparatus for converting X-ray images into viewable television pictures, thereby reducing X-radiation exposure of the viewed subject to lower, safer levels.

A further object of this invention is to provide an improved apparatus for converting ultrasound images into viewable television pictures.

A feature of this invention relates to a multiple layer target comprising a first layer or sheet of high dielectric material facing toward an electron gun, and a second layer or film of material responsive to radiant energy. The term radiant energy as used herein is to be interpreted in its rice broadest sense, and is intended to include among other things, light energy, X-ray energy, gamma ray energy, and ultrasound energy. The second layer or film is substantially non-conductive when not exposed to radiant energy, and exhibits a resistance variable with the intensity of radiant energy incident thereupon.

A further feature of this invention relates to an improved method for detecting variations 0r changes of potential on the surface of the high dielectric layer or sheet. The potential variations are sensed by means of a high energy electron beam and then converted to electrical signals for use with a television display apparatus.

A further feature of one preferred embodiment of this invention relates to a third layer for transducing X-radiation to photo-electrons which, in turn, act upon a second, gaseous layer or film so as to produce a tremendous amplification of the converted image.

Other features and advantages `will be apparent from a consideration of the ensuing description in combination with its accompanying drawing in which:

FIGURE 1 is a schematic daigram of an image transducing electron tube incorporating the features of the invention;

FIGURE 2 is an enlarged cross-sectional diagram of a target used for converting light images into television signals;

FIGURE 3 is an enlarged cross-sectional diagram of a target used for converting X-ray images into television signals; and

FIGURE 4 is an enlarged cross-sectional `diagram of a target used for converting ultrasound images into television signals.

Referring more particularly to FIGURE 1, there is shown an electron tube assembly 10 including an electron gun 12 situated at one end of an evacuated envelope 14, facing a target 20 supported at the opposite end of the envelope and arranged so that an electron beam 22 from the electron gun 12 impinges on the face of the target facing the electron gun While radiant energy images 26 impinge on the other face of the target. The electron gun 12 provides a high energy beam of electrons 22 which is scanned across the face of the target 20 by any suitable deflection means 30 to provide a raster. Secondary emission electrons 32 resulting from bombardment of the target by electrons from the electron beam are collected by a collector grid or mesh 36, conducted to an electron multiplier 40 which comprises means for detecting variations of current on said collector grid or mesh, illustrated by block diagram, and the resultant electric signal is delivered at lead 42.

Referring now to FIGURE 2, there is shown one pre-` ferred embodiment of the improved target structures of the invention. The target 44 shown is useful for transducing light images. Layer `46 is :a first layer or sheet consisting of a high dielectric material which may be any of the well-known insulators such as quartz,`glass, or barium titanate. A second layer or lm 50 consists of photo conductive material which is contiguous to and substantially coextensive with the first layer 46. The photoconductive layer or film 50 may be any of the well-known materials which are substantially nonconductive in darkness but which become conductive upon exposure to light. Such materials include but are not limited to the particular salts or metals such as cadmium sulfide, zinc sulfide, cadmium selenide gold doped germanium, antimony trisulphide, antimony trisulphide and zinc selenide. The outward facing surface of the photoconductive layer 50 is situated so as to receive a light image 52 focused thereupon. This light-facing surface is coated with a light transparent electrically conductive film 56 of any suitable material such as tin oxide. This coating is connected by a lead 58 to a source of positive direct current potential (not shown) which can be approximately 25 to 50 volts. By this means a positive potential is applied uniformly to the light-facing surface of the photo-conductive second layer 50 and a related potential appears on the face or surface of the high dielectric first layer 46 facing the electron gun. The exact potential at incremental areas on the face of the high dielectric layer 46 is governed by the resistance of corresponding areas of the photoconductive layer 50 which, in turn, is controlled by the intensity of light incident thereupon. Thus, there is formed on the surface of the first or high dielectric layer 46 a charge distribution comprising a variation or pattern of electrical potential corresponding to the pattern of light falling upon the photo-conductive layer 50. As electrons from the electron beam 22 sweeping across the face of the first layer 46 impinge upon incremental areas of varying potential, this variation of potential provides a corresponding variation in the amount of secondary emission, the number and distribution of the secondary emission electrons being correlated with the charges produced on the high dielectric layer by conduction through the energy-sensitive layer. The secondary emission electrons are collected on the collector mesh 36, and the resulting current variations or signals are amplified by the electron multiplier current variation detection means 40 shown in FIGURE 1. The resulting electric signal can be used to display an image on a television receiving apparatus.

In another preferred embodiment of this invention, means are provided for transducing an X-ray image into television signals Without the necessity of first converting the X-ray image to a light image. As illustrated in F G- URE 3, this embodiment of the invention utilizes a thr elayer target 70. The first layer or sheet 72 is a high dielectric material of the nature described above with reference to FIGURE 1. The second layer or film 76 consists of a gas mixture having such characteristics that it is normally nonconductive, but which becomes conductive at incremental portions when these portions are triggered beyond a saturation potential of the gas mixture. Such gas mixtures are of the type used in Geiger- Mueller counters and are well-known in the art. The gaseous second layer or film is a few tenths of a millimeter thick. A third layer 'or film 80 consists of metal of the type which emits photo-electrons upon X-ray excitation. A thin coating of lead evaporated on an aluminum plate has been found to be suitable for this purpose. This third layer 80 is situated adjacent that surface of the second layer 76 which faces the first layer 72. In this arrangement the second or gaseous layer 76 lies between the high dielectric layer 72 and the metallic layer 80. An electrical potential `of approximately 1000 volts is applied across this gas mixture, the exact potential being adjusted so as to charge the gas mixture to a point just below saturation level. The third layer 80 serves as the positive electrode for this purpose, being connected by a lead 84 to a positive potential source (not shown). The negative electrode is a mesh 86 supported within the gaseous second layer 76 adjacent to and substantially coextensive with the first layer 72 but sufficiently spaced therefrom so as to preclude electrical contact therewith. A lead 88 connects the mesh 86 to a corresponding negative potential source. Wall means 90` connect peripheral portions of the first and third layers to one another to define a chamber 94 enclosing and confining the gas mixture 76.

The operation of this embodiment of the invention is as follows: An X-ray image 96 from a source (not shown) .4 is projected onto the face of the metallic layer of the target 70. Photo-electrons thereupon dislodged from the metallic layer enter the gaseous second layer 76. A source of electrical potential (not shown) is applied across leads 84 and 88 and through'electrodes 80 and 86, maintaining the gas mixture charged to a potential just below its saturation point. Where the emitted photoelectrons enter the gas mixture 76, they trigger a saturation electrical discharge of the gas at incremental areas corresponding to the areas, pattern or image of X-ray excitation of the metallic third layer 80. Upon saturation, the gas ions produced electrically charge the high dielectric layer 72 in a pattern corresponding to the X-ray image impinging on the metallic layer 80. Finally, the pattern of electrical potential present on the surface of the high dielectric layer 72 is translated into an electrical signal in exactly the same manner as described above wtih respect to the first embodiment of the invention.

In an additional preferred embodiment of this invention, means are provided for transducing ultrasound irnages into viewable television signals. The 4basic structure ror ultrasound visualization systems is described in U.S. Patent No. 3,236,944. The invention herein described is an improvement thereon wherein an additional layer or sheet of material of high resistance is deposited upon the piezo-resistive materials of high sensitivity without sacrificing storage characteristics.

Illustrated in FIGURE 4 is a cross-sectional view of an ultrasound transducing target 102. A first layer or sheet 104 consists of a high dielectric material which may be any of the well-known insulators identified above. A second layer of film consists of piezo-resistive material which is contiguous to and substantially coextensive with the first layer or sheet 104. This piezo-resistive layer or film may consist of any of the well-known materials exhibiting piezo-resistive characteristics which materials include but are not limited to cadmium sulfide, zinc sulphide, zinc oxide, and titanium dioxide, as described in U.S. Patent No. 3,236,944, the entire disclosure of which is incorporated herein by reference to the extent that it is not inconsistent herewith.

The operation of this embodiment of the invention is as follows: An ultrasound image 116 is projected against the piezo-resistive layer or film 110 which is coated with an electrically conductive coating 106 connected 'by lead 114 to a source of positive direct current potential of approximately 25 to 50 volts (not shown). By this means a D C. potential is applied uniformly to the ultrasound facing surface of the piezo-resistive second layer on film 110 and a related potential appears on the face or surface of the high dielectric first layer or sheet 104 facing the electron gun. The exact potential at incremental areas on the face of the high dielectric layer 104 is dependent upon the resistance of corresponding areas of the piezo-resistive layer 110 which in turn is controlled by the intensity of ultrasound energy incident thereupon. A variation or pattern of electrical potential is thus formed on the surface of the first or high dielectric layer 104 corresponding t0 the ultrasound image 116 projected on the target. This pattern of electrical potential is translated into an electrical signal in the same manner as described above with respect to the first embodiment of the invention.

While this invention has been described in connection with three preferred embodiments, it is to be understood that the description is illustrative only and is not intended to limit the invention, the scope of which is defined by the appended claims.

What is claimed is:

1. In an electron tube apparatus:

an electron tube;

an electron gun mounted within said tube for providing a deflectable beam of electrons within said tube;

a. multiple-layer transducing target supported within said tube and spacially oriented to extend generally transversely of and in the path of said beam of electrons to interrupt electrons of said beam scanning said target and impinging thereagainst, said target comprising:

a rst layer consisting of a high dielectric material facing toward said electron gun to receive electrons beamed therefrom;

t a second layer contiguous to and substantially co-extensive with said first layer and disposed on a side of said first layer opposite said electron gun, said` second layer comprising a gas mixture normally non-conductive, and which is rendered conductive upon bombardment with photo-electrons;

a third layer contiguous to and substantially co-extensive with said second layer, said third layer 4fbeing selected from the group consisting of materials responsive to X-radiation impinging thereupon to emit photo-electrons;

whereby, upon bombardment of said third layer of X- radiation said third layer emits photoelectrons into said gaseous second layer;

means to impinge an X-ray image upon said third layer;

Wall means interconnecting peripheral edge portions of said first and third layers to define a chamber for containing said gaseous second layer;

said third layer also comprising a positive electrode for charging said gaseous second layer to a value just below a threshold corresponding to a saturation level;

a mesh comprising a corresponding negative electrode supported in said gaseous second layer adjacent to said first layer and extending generally parallel thereto;

a D.C. source of electrical potential connected between said positive electrode and said negative electrode;

whereby photo-electrons emitted from portions of said third layer and entering said gaseous second layer are effective to overcome said threshold and to trigger incremental portions of said gaseous second layer to conduction;

said conducting incremental portions of said gaseous second layer defining a pattern corresponding to said image projected against said third layer to provide a charge pattern on said first layer of said target;

means for deflecting the electron beam of said electron gun for scanning said first layer with electrons from said gun to effect emission of secondary electrons from said first layer;

secondary electron collector means mounted Within said tube adjacent said target for collecting secondary electrons emitted from said first layer in response to electron bombardment thereof;

means for detecting changes in current flow to said collector means corresponding to variations in the number of said secondary electrons emitted from said first layer;

said variations in said number of emitted secondary electrons being correlated with and dependent upon a charge pattern formed on said first layer by corresponding variations in potential of portions of said high dielectric material, said variations resulting from increase and decrease in conductivity of said incremental portions of said second layer in response to corresponding variations in X-ray energy incident upon said third layer;

thereby producing an output signal from said apparatus representative of said X-ray energy and corresponding to the X-ray energy excitation of said third layer; and

means to conduct said output signal from said apparatus.

2. In an electron tube apparatus:

an electron tube;

an electron gun mounted within said tube for providing a deflectable beam of electrons Within said tube;

a transducing target supported within said tube and spacially oriented to extend generally transversely of and in the path of said beam of electrons to interrupt electrons of said beam scanning said target and impinging thereagainst, said target comprising;

a first layer consisting of a high `dielectric material facing toward said electron gun to receive electrons beamed therefrom;

a second layer contiguous to and substantially coextensive with said first layer and disposed on a side of said first layer opposite said electron gun, said second layer comprising a piezo-resistive material normally substantially nonconductive when not exposed to ultrasound energy incident thereupon;

means for applying a D.C. source of potential to said piezo-resistive material to establish a biasing potential on said high dielectric material of said first layer of said target;

means to impinge an ultrasound image upon said second layer, thereby causing incremental portions of said second layer to conduct;

said conducting incremental portions of said second layer defining a pattern corresponding to said ultrasound image projected against said second layer to provide a charge pattern on said first layer of said target;

means for deflecting the electron beam of said electron gun for scanning said first layer with electrons from said gun to effect emission of secondary electrons from said first layer;

secondary electron collector means mounted within said tube adjacent said target for collecting secondary electrons emitted from said first layer in response to electron bombardment thereof;

means for detecting changes in current flow to said collector means corresponding to variation in the number of said secondary electrons emitted from said iirst layer;

said variation in said number of emitted secondary electrons being correlated with and dependent upon a charge pattern formed on said first layer by corresponding variations in potential of portions of said first layer, said variations resulting from increase and decrease in conductivity of said portions of said second layer in response to corresponding variations in ultrasound energy incident upon said second layer;

thereby producing an output signal from said apparatus representative of said ultrasound energy and corresponding to the ultrasound energy excitation of said second layer, and

means to conduct said output signal from said apparatus.

3. A method of converting a pattern of X-ray energy to a visual image, said method comprising the steps of:

beaming a stream of electrons through a cathode ray tube to form a scanning raster on a layer of high dielectric material;

impressing a D C. potential across a gaseous layer disposed adjacent said high dielectric layer on a side opposite said stream of electrons, said gaseous layer being normally non-conductive but being rendered conductive upon bombardment by photo-electrons;

applying an X-ray image to a metallic layer overlying said second layer, said metallic layer being responsive to said X-ray image to emit photo-electrons into said gaseous layer, thereby charging said high dielectric layer at incremental portions corresponding to said pattern of X-ray energy; and

detecting variations in secondary emission electrons energy to a -visual image, said method comprising the steps of:

beaming a stream of electrons through a cathode ray References Cited gabe to. form a'sc'anning raster on a layer of high UNITED STATES PATENTS ielectric material,

impressing a D C. potential on a piezo-resistive layer 2,863,087 12/ 1958 Barbier 315-11 disposed adjacent said high dielectric layer on a side 5 2,866,918 12/ 1958 Hansen 315-11 opposite said stream of electrons; 2,903,617 9/1959 Turner 313--89 X applying an ultrasound image to said piezo-resistive 3,136,909 6/ 1964 Cope.

layer, rendering said piezo-resistive layer conductive rat incremental portions thereof, thereby charging RODNEY D. BENNETT, JR. Primary Examiner said high dielectric layer at incremental portions cor- 10 responding to said pattern of ultrasound energy; and R' E BERGER Asslstant Exammer detecting variations in secondary emission electrons U S Cl X R emanating from said high dielectric layer for display on a television receiver. Z50-83.3, 213; 313-65, 89

UNITED STATES PATENT omiten- CERTIFICATE OF CORRECTION Patent No. 3,505,558 April 7, 1970 John E. Jacobs It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column l, line 27, insert The invention described herein was made 1n the Course of work under a grant or award from the Department of Health, Education, and Welfare.

Signed and sealed this 29th day of December 1970.

(SEAlJ fittest:

Edward M. Fletcher, if. WILLIAM E. SCHUYLER, JB.

Attesting Officer Commissioner of Patents UNITED STATES .PATENT oFFCEv CERTIFICATE OF CORRECTION Patent No. 3,505 ,558 April 7 1970 John E. Jacobs It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column l, line 27, insert The invention described herein was made in the course of work under a grant or award from the Department of Health, Education, and Welfare.

Signed and sealed this 29th day of December 1970.

(SEAL) Attest:

WILLIAM E. SCHUYLER, JR.

Commissioner of Patents Edward M. Fletcher, Jr.

Attesting Officer 

